Fading regulator



Aug. 20, 1935.

H. J. J. M. DE R. DE BELLESCIZE FADING REGULATOR Filed Aug. 25, 1930 SIGA/Al /NPU T INVENTOR H.\LJ. M. e K de BELLESCIZE BY /w fpm/W ATTORNEY Paeses as. ze, 1593559, 1

man'

- America, New 'Y Delaware York, N. Y., a corporationof aseiiejuonnugustes, 19st, serial No. 477,312

Y v lin FranceSeptember'4, 1929 3 anims.v (Ci. 25o-20)'Y The present inventionrelates to systems lor leliminating fading effects and suitable arrangef ments of circiiitsior accomplishing the results.

Offft'h'e devices conceived for thepurposeof reV4 ducing the 'fading almost all have'one important faultinherent inv the very nature of the problem Y to be solved'.` This fault consists, infact, in cor-V f rectingthe changes Vin the carrier V-vvave dueto Ufading, 'at the",s arr1 e `time not iniiuencingthose which are due to the modulationwhich consti# tutesV the fsignal.Y Hence, the necessity arisesto] introduce at sume pointatirne constant orfairly.` v high value.: In suchacase correct results yare" obtained'ii the speed of .the variations which the iadingfirnpresses upon theV carrier Wave `is always smaller in'c'omparisonfto `those which correspond to.' the .various 'frequencies o the modulation;

This isnot always the case and the outcome is that the adjusting deviceA acts in retarding m`anner oieven'in opposed'sense.

, In acc rdance withthe present invention, this fault lrnay ,be oorrectedby adding to the. adjusting device a restricting device limiting',Whatever may happen,` the voltage verationapn which the sensitivityof the receiver vdepends, to th e values strictly :necessary orproducing the, desired result.

f Two einbodirnents 4have been shown by the acel A Acompanying drawing: the one, illustrated by Figs 1-'2-3, concerns the'anti-fading device inr which thev detected current influences the sensitivity of the yinputelementsV by means. oi a tube with sev-,S

eral electrodes;` the other, illustrated by Figs. 4 and 51 concerns an anti-fading device which the'saine result is achieved by means oanl electro-,mechanical relay. In Fig. 1, the h. oscillations constituting the signal arrive at I, subsequent to their passage through the usual .receiving elements such as the antenna, resonators, andthe like. This receiver is suppliedvwith energyfrorn the local sources- 2-3-d. The incoming signaloscillations iniiuence, for instance by means of transiormerssuch as 5, one or several tubes, one. oiits, or tli'eir,` Y electrodes, controlling thesensitivity Aof the corresponding amplification stage, v being impressed with the pctentialexisting .at the extremity ofv a resistance 23, traversed by the detected current.k

The detection'is accomplished by means of one of the methods known in the'priorfart, forinl stance by means of the shunted condenserI 8 3,Y

connected inseries With the grid of tube l i. l A

connection l2, liti, itfthen transmits the modu-Y lation'oi the carrier Wave Vto tube itfpreferably polarized or biasedv at 16,. The output fromA tube i8 is'then directed 'to 'the recording :device "19 .the usual 'circuit arrangenient'A isrnodie'd inthe which may-consist of 'a telegraphic relayv or a;

telephone apparatus. j x

Inrparallel with these circuitsofflow yfrequenrzy is disposed the device insuring `the correction of the fading: the grid or" a `tube 2t is connectedto of an v'adjustable source 2l -which insures the polarization. The plate-circuit of tube 2 6 vcoinprises the resistance 23,and the con-denser 22, the

' the `top end of a 'resistance' i2 Withthe insertion noY eect in an' ordinary antieiadingfdevice, This source 2t will be preferably placed between *the resistance .2 3 and the plate lin order lto` eliminate a polarizationcell, Which'would be disposed ad,- justably in the conductor,connectingl the resiste ance-23 to the grid of tube 5. In this circuit arr any increase in the 'intensity Iof the carrier. wave extremity of thel'resistance l2 4and "thereioreiat the grid of 2&3; only one manipulation will have to be done andy that is theadjustrnent of the-tap l2l inthe manner that the plate circuit of 20 begins to discharge as soon as thel carrier wave reaches the desired limit. This'discharge causes a po' tenti-al drop at 23, hence, a desensibilization of the ,amplierstage 6; l 'P .A

'-Thef'fault, which the invention proposes to rectify, appears when a fading suddenly' suc ceeds an increase and then areduction the intensity of the signah` start of ,thepheef nomenon-increase in the intensity of the Isignal carrienfior tube -Zlan elevation in the grid potentialand the generation of anintense plate current which can not be reduced at allier the reasonV that theV timey constant .ofgthfe assembly 22--23 prevents theirnniediate desensibiliaation denser 22 reduction in rthe intensity of the signal finds the;

regulator'then in a poor. operatingzcondition, Vinl fact,inu spite ofthe potential drop at the grid of.

tube, 20, the resistance Ztis still traversed'byfa current `originating from the fdischargeof the quantity of electricitystor'ed inthecapacity 22.` Accordingly, the receiver continues Vto be ydesensibilized ,byfthe anti-fading which acts, no't `any more retardingybut in lopposite sense and a more' or less long `part ofthesignalissnotlrecorded atm `For -the purpose of reinedy'ing "this situation rangement, representing nothing neWupjto-now, l

' further Ve=028, the polarization annulling the sensitivity, and Ro the value of the resistance 23. The maximum current to dischargerin the resist-V ance 23 has the value:

Consequently the tube V2l) acts as restricting tube in the manner that its characteristic reaches the top at the amplitude. 0-29=Io (Fig. 3). All

that is necessary to accomplish this is tofdispcse a high resistance 25 in series with its "grid (which produces the effect, as is known, to establish'a bend in the characteristic), and to adjust carefully its platepotential u` with the' aid'rofthe tap 26; a too strong a potential Yug` (Fig. r3)- would leave a `partof Ythe fault stillremaining, whose nature has 'just beenV explained; a too feeble a potential u1 would not allowra suilicientV desensibilization of the tube 6. v

A resistance 24 of relatively large sizecompared to `23Y completes the device; it has the func-tion of permanently shunting the source 26,

even if `Vtube 20 is polarized greatly in the negative sense. `This has the effect of producing inl resistor `23 and, consequently, at the grid of tube` 6,1an initial potential drop such as 0-727 (Fig. 2)

e corresponding to a point of the characteristic of this tube reaching practically'its maxirnuni` in# clination.. Thus, any sudden increase in the'intensity of the signal, which might cause the tube 2G vto discharge, is revealedrby an immediate effective increase of the polarization of tube 6.- In this manner 'the `retarding effects of thefantifading regulator areu reduced.

The example according to Figs. 4 and 5 concerns'devices with electromechanical relay. Thel sensitivity of the` amplification stage 6 depends in this case onY the potential v at the terminals of a condenser 30, the latter being charged in turn bythe action of a relay 32 connecting the same, across the resistances 35-36; with the ene or the other of the taps 3l-38; one corresponds (Fig. 5) vto the potential 0-47f-'forwhich the characteristic -of tube 6 lhas 'practically reached its maximum inclination; Ythe othenat the v'potential 0fi8,` nullifies the sensibility.' The relay itself is energized by a coil 40,-traver7s`ed' by the detected current of the carrier wave: An adjustment, for instance, the one of the auxiliary coil 4I and of rheostat 43, is thev means for ad-V iusting the` relay in the' manner that-its armature is in a state of equilibrium between the con- Y tacts .3a- 34 whn'the carrier wave has the exact desired amplitude.

A very apparent fault is observed in telephony; a sudden increase in the intensityof the signal, subsequent to a strong fading, Vproduces a reportf in the telephone receivers.v VThis phenomef non may be explained as followsziduring a fading,ymakingjuse ofthe entire'sensitivity of the receiver, the detected current decreases and the armature 3| will bear against Acontact 33, ref

leasing, with the aid of tap'31, a potential such as 0-4l7 Y(Fig.V 5); the condenser 30 tendsto' acv quire 'this potentin and the sensitivity' ofthe .tub 6 increases; this increase, at firstrapid, becomes slower and slower for the reasonthat, on'the one hand, while it moves on the characteristic in the sense indicated by the arrow, the curvature varies les's'and less quickly; on the other hand, the potential vat the terminals of condenser 3S, being produced according to an exponential law, Varies slower `and slower'in proportion as it approaches the asymptotic limit .il-47. I-Ience, it is necessary to dispose this limit to thel `extreme right (Fig. 5)Y of 'the potential' o eo'for 'which Vthe inclinationl of the characteristic comes within the vicinity of its maximum. But assur'ning now a sudden increase in the intensity succeed-V ing the Yfading andproducing the release of the armature of the relay with the result'that the Source ,(30 :of the potential 0-48 enters into action; during vthetime which the charge 'u of vcondenserv 3,0 requires for traversing the interval 414,50, the sensitivity is subject to only a slight decrease; hence the report heard at the receiverr For the prevention of this phenomenon there maybe employed, according to the invention, `an

auxiliary tube lili whose grid is impressed with the potential@ of condenser 3 9, and the plate with a potential so that the lower start of theV characteristic g=f (o) takes place (Fig. 5)

for a grid potential which is very close tothe value 0-50. f This plate current 7' will be *sentv into an auxiliary coilAZ of the relay for the purpose of drop'r'iingv the armaturetowards the desensibilization' lcontact 34. In lthis manner the potential of condenser 3G is, whatever may hap- ',pen, automatically limited to the higher value `0-50. Under .the effect A,of a strong fading fol-4 lowed by a sudden increase in the intensity of the signal, the adjustment is now accomplishedY as follows: During the fading, the armature first establishes thefcontactf andyputs :into action the potential source OV-ll'l;v this vpotential Vmay have `a high value and may even belpositive sincev thefpotential v of thecondenser willnot reach it; hence, the increase .offra is very rapidy andn the fading correctedv with optimum `results. When v reaches the value 0-50, itdoesnot have toexceed it, since it corresponds to the limit of sensitivity ofthe amplier stage. rIhen the current y' of theauxiliary 'valve 44 enters into action, `the armature leaves the contact 33 and, as long as it is not influenced by a change, remains in the state-of equilibrium. Afterwards, thesudden increase in the intensity subsequent to the fading, attracts the former towards contact 34, releasing for action the potential source 0-48; the charge 'udecreases and this decrease, starting from the value ile-50, at once Aproduces the one of thesensitivitm hence, the correction of the `regulator again isin the right direction, the

report in the receiver disappears.l Y

Whilev the invention has been described in c onnect-ionrwith two Yof its preferred'embodiments,

cation, means for detection including an input and output circuit, means f o-r controlling the radio frequency gain by a potential which varies e depending upon the value of theV detected curo l 2,011,930 y rent, said last means comprising an electron dis4 amplification means for controlling the `ampliiicharge device having a control electrode adaptedl to receive the detected currents `and an anode circuit,V and a connection connecting said control electrode only With the output circuit of said detection means, a resistance and a condenserconl nectedr in parallel to said resistance and associatedovvith theV anodecircuit of said electronv dis.

charge device, said anode circuit being connected with said radio frequency amplication means vand ladapted to supply said potential for con#- trolling the radio frequency gain, said resistance and condenserbeing responsive toa maximum value of current flowing in said anode circuit to control said value of potentialto reduce the Vamount of radioy frequency amplication to zero,

andseparate means for establishing the minimumv and maximum current supplied by the said Vdischarge. device at such values that the control currents, means to detect radio frequency cur- Y' .vice connected to the Youtput circuit of saidfden f rents, saidv last means having anfinput circuit andan output circuit, an electron discharge de-I .Y tection means and adapted to be controlled by the detected currents and having an anode, a

Vcathode and a control electrode, a high time-- vconstant circuit constituting alresistance and a capacity in shunt of said resistance associated.. with said anode andwith said radiofrequency cation thereof, a resistance connected to the control electrode of said electron discharge device and having such value as to limit the maximum current in the input circuit of said device such that the current flowing through the resistance of the high time-constant circuit, sets up a Vpotential strictly necessary to reduce the radio frequency amplification to Zero, and another resistance directly connecting said cathode and said anode and having a value such that when the detected currents are of maximum value a po tential is set up corresponding to the beginning of the maximum slope rof lthe characteristic of the, radio, frequency amplification means.

this characteristic .to limit in the two directions variations of the said output current, said means comprising a circuit arrangement whereby one end of the said non-linearV characteristic'is adjusted to reduce to zero theminimum radio frequency gain, and the other 'end of the said nonlinear characteristic is'adjusted to raise the maxi;-v mum radio frequency gain to a .predetermined value,v and a high timefconstant lcircuit associat-A ed with thefoutputof the said electron tube and connected with the input ofthe said amplifier for controlling the radio frequency gain accord-1 ing to the variations current.

of the said limited output v15 3. In an anti-fading receiver for electromagnetic Waves, a radio frequency amplifier, a def 

